On 12/04/2013 05:09 PM, Konrad Rzeszutek Wilk wrote:
On Wed, Dec 04, 2013 at 10:10:28AM +0100, Daniel Lezcano wrote:
On 12/03/2013 10:33 PM, Rafael J. Wysocki wrote:
On Tuesday, December 03, 2013 10:59:58 AM Konrad Rzeszutek Wilk wrote:
If not, we could end up in the unfortunate situation where
we dereference a NULL pointer b/c we have cpuidle disabled.
This is the case when booting under Xen (which uses the
ACPI P/C states but disables the CPU idle driver) - and can
be easily reproduced when booting with cpuidle.off=1.
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff8156db4a>] cpuidle_unregister_device+0x2a/0x90
.. snip..
Call Trace:
[<ffffffff813b15b4>] acpi_processor_power_exit+0x3c/0x5c
[<ffffffff813af0a9>] acpi_processor_stop+0x61/0xb6
[<ffffffff814215bf>] __device_release_driver+0fffff81421653>]
device_release_driver+0x23/0x30
[<ffffffff81420ed8>] bus_remove_device+0x108/0x180
[<ffffffff8141d9d9>] device_del+0x129/0x1c0
[<ffffffff813cb4b0>] ? unregister_xenbus_watch+0x1f0/0x1f0
[<ffffffff8141da8e>] device_unregister+0x1e/0x60
[<ffffffff814243e9>] unregister_cpu+0x39/0x60
[<ffffffff81019e03>] arch_unregister_cpu+0x23/0x30
[<ffffffff813c3c51>] handle_vcpu_hotplug_event+0xc1/0xe0
[<ffffffff813cb4f5>] xenwatch_thread+0x45/0x120
[<ffffffff810af010>] ? abort_exclusive_wait+0xb0/0xb0
[<ffffffff8108ec42>] kthread+0xd2/0xf0
[<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180
[<ffffffff816ce17c>] ret_from_fork+0x7c/0xb0
[<ffffffff8108eb70>] ? kthread_create_on_node+0x180/0x180
This problem also appears in 3.12 and could be a candidate for backport.
CC: "Rafael J. Wysocki" <[email protected]>
CC: Daniel Lezcano <[email protected]>
CC: [email protected]
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Applied, thanks!
---
drivers/cpuidle/cpuidle.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 2a991e4..a55e68f 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -400,7 +400,7 @@ EXPORT_SYMBOL_GPL(cpuidle_register_device);
*/
void cpuidle_unregister_device(struct cpuidle_device *dev)
{
- if (dev->registered == 0)
+ if (!dev || dev->registered == 0)
return;
cpuidle_pause_and_lock();
Oops, wait. Are we sure the problem is coming from cpuidle ?
It is acpi_processor_power_exit assuming that the cpuidle is
initialized. It could be fixed there too, but there are multiple
entries in cpuidle where it does the : "if (!dev) return .."
so I figured this should be done as well here.
I understand.
From my POV the bug is coming from the acpi processor idle driver.
The function acpi_processor_power_init registers the cpuidle driver and
the cpuidle device when acpi_processor_registered is zero. Then it
increments acpi_processor_registered preventing the next call to this
function to register the driver but it will register the device.
As cpuidle is disabled, the cpuidle_register_driver fails, thus the
device is not registered and acpi_processor_registered is not
incremented. So all calls to acpi_processor_power_init prevents the
driver and the device to be registered. No problem with that.
But the function acpi_processor_power_exit does not take care of the
value of acpi_processor_registered and just unregister the device. Then
it decrements acpi_processor_registered which is zero to -1.
Trying to be immune from a NULL pointer in cpuidle_unregister_device
hides bogus code from the caller. So IMO, this check shouldn't be there
and the acpi_processor_power_exit function should be fixed instead.
The cpuidle_unregister_device is called with a NULL pointer, that
shouldn't happen.
It does :-)
Konrad, you say that could be easily reproduced. How do you produce
it ? Unplugging a cpu ?
Yes.
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